1. Field of the Invention
The present invention relates to a method and system of specifying an abnormality cause in the fabrication process of a product, and a semiconductor device fabrication method.
2. Description of the Related Art
One of the largest problems to be solved to increase the productivity of products, e.g., semiconductor devices is to increase the yield. To increase the yield, it is important to analyze the yield loss, and find and improve the process, fabrication apparatus, or design condition which is used in the fabrication process having caused the loss, in the early stages. However, semiconductor devices, particularly, semiconductor integrated circuits (LSIs) are produced through hundreds of fabrication steps and fabrication apparatuses. Once a defective LSI is produced, therefore, it is generally very difficult to specify the abnormality cause of the defective product.
The results of a wafer test which is a semiconductor device electrical characteristic test conducted after the wafer process is completed sometimes gives an important clue to find an abnormality cause. This is so because the wafer process and wafer test are performed with a plurality of semiconductor devices being kept arranged on a round wafer. A position where a defective semiconductor device is produced on the wafer surface is specified by indicating the results of the wafer test as positions in the plane of the wafer by mapping. A representative mapping indication is a fail bit map (FBM) obtained for memory products. Also, a pass/fail map which indicates each good product (pass) and each bad product (fail) by mapping is used for logic products or memory embedded logic products.
In these fail bit map and pass/fail map, defect distributions in the plane of a wafer are roughly classified into a random defect distribution in which defects evenly distribute regardless of positions on the wafer surface, and a clustering defect distribution in which positions on the wafer surface are biased. Of these distributions, the clustering defect distribution is in many cases caused by the process, fabrication apparatus, or the like as an abnormality cause. This clustering defect distribution is regarded as a “fingerprint” of an abnormality cause resulting from the process or fabrication apparatus. That is, if an abnormality occurs in a certain process or fabrication apparatus, defective products having a clustering defect distribution unique to the process or fabrication apparatus are produced.
From the foregoing, an abnormality cause in the fabrication of semiconductor devices can be specified by specifying a fabrication apparatus used in certain steps of the fabrication process in common, for a plurality of wafers in which the same clustering defect distribution occurs, or for a plurality of lots formed by these wafers (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2004-288743).
Unfortunately, there are hundreds of semiconductor device fabrication steps. To make it possible to specify an abnormality cause in each individual fabrication step, therefore, it is necessary to acquire various data in these fabrication steps and in inspection steps before and after the fabrication steps, and this makes the data amount enormous. The enormous data makes it very difficult to select data which is truly significant to specify an abnormality cause, thereby making specification of an abnormality cause impossible.